Camera with image stabilization controlled by focus detection

ABSTRACT

A camera includes a vibration detecting sensor for detecting a vibration of the camera, a correcting device for correcting a shake of an image due to the vibration, a focus detecting circuit for detecting a state of focus by using information about the image, and a controlling circuit for controlling the correcting operation of the correcting device according to the state of focus detected by the focus detecting circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a camera provided with an imagestabilization function.

2. Description of the Related Art

In recent years, the evolution of video apparatus, such as videocameras, is remarkable, and automation and a greater number of functionshave been realized in various aspects of the video apparatus, One recentexample has been the realization of a video camera provided with animage stabilization device which enables good photography by correctinga shake of an image due to a vibration of the camera. FIG. 1 is a blockdiagram of one example of a camera provided with an optical imagestabilization function.

The example shown in FIG. 1 includes a light deflecting lens (variableangle prism) 101 for optically correcting the displacement of an opticalaxis and performing an image stabilization operation. The structure ofthe light deflecting lens 101 is such that, for example, a spacesurrounded by two flat sheet glasses and a bellows is filled with aliquid essentially consisting of silicone. The light deflecting lens 101is arranged to perform two-dimensional deflection of light by therespective two sheet glasses being pressed vertically and horizontallyby corresponding actuators which will be described later.

The example shown in FIG. 1 also includes an angular-velocity sensor 102for detecting a vertical vibration, an angular-velocity sensor 103 fordetecting a horizontal vibration, an image stabilization control circuit104 for correcting a shake of an image due to a vibration by controllingthe light deflecting lens 101 on the basis of vibration informationsupplied from the angular-velocity sensors 102 and 103 and varying thedirection of refraction of light, a driver 105 for outputting an outputfor driving the light deflecting lens 101 to vertically deflect light,an actuator 106 for driving the light deflecting lens 101 in accordancewith the output of the driver 105, a driver 107 for generating an outputfor driving the light deflecting lens 101 to horizontally deflect light,an actuator 108 for driving the light deflecting lens 101 in accordancewith the output of the driver 107, an apex angle sensor 109 fordetecting the amount of vertical deflection of light by the lightdeflecting lens 101, and an apex angle sensor 110 for detecting theamount of horizontal deflection of light by the light deflecting lens101.

The example shown in FIG. 1 also includes a focus adjusting lens 111, animage pickup element 112 such as a CCD, an amplifier 113, a high-passfilter 114 for extracting a high-frequency component which varies withthe state of focus, from a video signal outputted from the image pickupelement 112, a lens control circuit 115 for moving the focus adjustinglens 111 toward an in-focus position, i.e., so that the level of thehigh-frequency component can reach a maximum, in accordance with thestate of the output signal of the high-pass filter 114, a motor driver116, and an actuator 117.

FIG. 2 is a graph showing the output level of the high-pass filter 114with respect to the position of the focus adjusting lens 111 in thearrangement shown in FIG. 1. As is known, the output signal level of thehigh-pass filter 114 has the feature that if the focus adjusting lens111 is out of focus, the high-pass filter 114 outputs a low-level signaland, if the focus adjusting lens 111 is in focus, the high-pass filter114 outputs a maximum-level signal. The lens control circuit 115utilizes such a feature and performs so-called "hill climbing AF"control for driving the focus adjusting lens 111 so as to make theoutput signal level of the high-pass filter 114 closer to a maximum.

FIG. 3 is a flowchart showing a specific process of the hill climbing AFcontrol. In the flowchart shown in FIG. 3, if the process is started inStep 401, the process waits for arrival of a vertical synchronizingsignal in Step 402. This is because, during each vertical synchronizingperiod, an image signal for one picture can only be obtained from avideo signal supplied from the image pickup element 112. If the arrivalof the vertical synchronizing signal is confirmed in Step 402, theoutput signal level of the high-pass filter 114 at that time is, in Step403, inputted into the lens control circuit 115 as a focus voltage valueindicative of the state of focus. In Step 404, on the basis of theinputted focus voltage value (by using a past voltage value asrequired), the lens control circuit 115 determines whether the focusadjusting lens 111 is currently located in an in-focus position. In thecase of a largely out-of-focus state in which the focus adjusting lens111 is entirely away from the in-focus position, the process proceeds toStep 406 through Step 405. In Step 406, the lens control circuit 115makes an analysis to detect whether an in-focus point is present on ainfinity-distance side or a closest-distance side, and drives the focusadjusting lens 111 to cause it to move at a high speed toward the sidedetected through the analysis. If it is determined in Step 408 that thefocus adjusting lens 111 is not largely out of focus and is present inthe vicinity of the in-focus point, the lens control circuit 115executes the processing of Step 409 to confirm the direction in whichthe focus adjusting lens 111 is to be driven. In Step 410, the focusadjusting lens 111 is driven at a low speed. The reason why the drivingspeed of the focus adjusting lens 111 is lowered in the vicinity of thein-focus point is to minimize the amount by which the focus adjustinglens 111 overruns the in-focus point.

If it is determined that the current position of the focus adjustinglens 111 coincides with the in-focus point, i.e., if the result of thedecision made in Step 405 is "NO" and the result of the decision made inStep 408 is "NO" and the result of the decision made in Step 411 is"YES", the focus adjusting lens 111 is made to stop in Step 412, and theprocess returns to Step 402. If it is not determined in Step 411 thatthe current position of the focus adjusting lens 111 coincides with thein-focus point, this indicates that it may be necessary to again performa focusing operation because of, for example, the movement of a subject.Accordingly, the process proceeds to Step 413, in which it is determinedwhether it is necessary to restart driving of the focus adjusting lens111. If it is necessary to restart driving of the focus adjusting lens111, i.e., if the result of the decision made in Step 413 is "YES", theprocessing of Step 414 is executed to confirm the direction in which thefocus adjusting lens 111 is to be driven. In Step 415, the lens controlcircuit 115 selects a driving speed suitable for the restarting. Then,the process returns to Step 402.

Since the image stabilization device and an automatic focus adjustingdevice are disposed as control systems independent of each other, theimage stabilization device continues its image stabilization operationduring the above-described focusing operation.

In the above-described related-art example, however, since the lightdeflecting lens 101 performs the image stabilization operation at alltimes, if the driving direction of the focus adjusting lens 111 is to bedetermined when the focus adjusting lens 111 is largely out of focus andthe focus voltage value is considerably low, the focus voltage value mayvary owing to a periodical, light deflecting action, for a cause otherthan the movement of the focus adjusting lens 111, so that an erroneousdecision may be made as to the driving direction.

During the largely out-of-focus state, since the contour of an image isentirely unsharp, the influence of an unnecessary vibration, such as avibration of a camera, upon photography is extremely small and theeffect of the image stabilization operation is low. In addition, in thecase of an image-stabilization camera integrated type video taperecorder, the possibility that a photographer starts photography duringthe largely out-of-focus state is comparatively low. For these reasons,the execution of the image stabilization operation during the largelyout-of-focus state offers many demerits to the processing of theautomatic focus adjusting device or the consumption of a power sourcesuch as a battery.

SUMMARY OF THE INVENTION

A first object of the present invention which has been made to solve theabove-described problems is to realize optimization of an imagestabilization function and an automatic focus adjusting function in acamera provided with the image stabilization function.

A second object of the present invention is to prevent malfunction ofthe image stabilization function and realize highly accurate imagestabilization characteristics.

A third object of the present invention is to optimize the operation ofthe image stabilization function and decrease power consumption.

To achieve the above objects, in accordance with one aspect of thepresent invention, there is provided a camera provided with an imagestabilization device, which camera comprises detecting means fordetecting a vibration of the camera, correcting means for correcting ashake of an image due to the vibration, focus detecting means fordetecting a state of focus by using information about the image, andcontrolling means for controlling execution and stop of a correctingoperation of the correcting means according to the state of focusdetected by the focus detecting means.

In accordance with another aspect of the present invention, there isprovided a camera provided with an image stabilization device, whichcamera comprises vibration detecting means for detecting a vibration ofthe camera, correcting means for correcting a shake of an image due tothe vibration, focus detecting means for detecting a state of focus byusing information about the image, and controlling means for varying acharacteristic of a correcting operation of the correcting meansaccording to the state of focus detected by the focus detecting means.

In such a camera, if an automatic focus adjusting device determines thatthe state of focus is a largely out-of-focus state in which an imagestabilization effect is small, response performance is lowered toprevent a focus detecting operation from being adversely influenced aswell as to reduce power consumption. If the automatic focus adjustingdevice indicates that the state of focus is an in-focus state or avicinity of the in-focus point, an image stabilization operation isexecuted and the response performance is enhanced so that a sufficientimage stabilization effect can be obtained. Accordingly, it is possibleto realize a good, stable image stabilization operation and focusadjusting operation.

The above and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof preferred embodiments of the present invention, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing one example of a camera provided witha general image stabilization device;

FIG. 2 is a characteristic chart showing the relationship between theposition of a focus adjusting lens and a focus voltage value;

FIG. 3 is a flowchart showing a focus adjusting process;

FIG. 4 is a block diagram showing the arrangement of each of first andsecond embodiments of a camera provided with an image stabilizationdevice according to the present invention;

FIG. 5 is a flowchart showing the processing operation of the firstembodiment of the camera provided with the image stabilization deviceaccording to the present invention; and

FIG. 6 is a flowchart showing the processing operation of the secondembodiment of the camera provided with the image stabilization deviceaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of a camera provided with an image stabilizationfunction according to the present invention will be described below indetail with reference to the accompanying drawings.

FIG. 4 is a block diagram showing the arrangement of each of first andsecond embodiments of the camera according to the present invention. InFIG. 4, identical reference numerals are used to denote constituentparts identical to those shown in the block diagram of FIG. 1, anddescription further thereof is omitted.

The arrangement shown in FIG. 4 includes a lens control circuit 118 forperforming an automatic focus adjusting operation, an imagestabilization control circuit 120, and a communication path 119 throughwhich the lens control circuit 118 can output an instruction to executeor stop an image stabilization operation to the image stabilizationcontrol circuit 120.

The lens control circuit 118 has a processing program for automaticfocus adjustment which is basically similar to that described previouslywith reference to the flowchart shown in FIG. 3. However, the processingprogram includes, in addition to the steps shown in FIG. 3, the steps ofoutputting through the communication path 119 an instruction signal tocontrol (execute or stop) an image stabilization operation according tothe state of focus.

The operation of the image stabilization control circuit 120 is similarto the image stabilization operation of the image stabilization controlcircuit 104 of FIG. 1. However, the image stabilization control circuit120 includes, in addition to the arrangement of the image stabilizationcontrol circuit 104, an arrangement for controlling (executing orstopping) an image stabilization operation according to an instructionsignal outputted from the lens control circuit 118 to the imagestabilization control circuit 120 through the communication path 119.

FIG. 5 is a flowchart showing a control operation according to the firstembodiment. In FIG. 5, identical reference numerals are used to denotethe steps of executing processings identical to those executed in thecorresponding steps of the flowchart of FIG. 3, and description thereofis omitted.

The flowchart of FIG. 5 differs from that of FIG. 3 in that the imagestabilization operation is controlled (executed or stopped) according tothe state of focus during the execution of the processing of automaticfocus adjusting control.

Specifically, if it is determined in Step 405 that the focus adjustinglens 111 is largely out of focus, the processing of Step 502 is executedso that the lens control circuit 118 communicates an instruction to stopan image stabilization operation to the image stabilization controlcircuit 120 through the communication path 119, thereby stopping theimage stabilization operation. This is because, in the case of such alargely out-of-focus state, a focus voltage value is expected to beconsiderably low as described previously so that if the light deflectinglens 101 is driven to perform an image stabilization operation, thefocus voltage value varies owing to a periodical, light deflectingaction and the lens control circuit 118 may erroneously determine thedirection in which the light deflecting lens 101 is to be driven. Thisis also because, in the case of the largely out-of-focus state, thecontour of an image is unsharp and an unnecessary vibration, such as avibration of the camera, does not exert a large influence on the imageso that the image stabilization effect is low. In the processing of Step502, it is also possible to prevent unnecessary power consumption.

If it is not determined in Step 405 that the focus adjusting lens 111 islargely out of focus and it is determined in Step 408 that the focusadjusting lens 111 is located in the vicinity of an in-focus point, thisindicates that the contour of the photographed image is considerablysharp and a remarkable, image stabilization effect can be visuallyconfirmed in an image plane. Accordingly, the process proceeds to Step501, in which the lens control circuit 118 communicates an instructionto execute an image stabilization operation to the image stabilizationcontrol circuit 120 through the communication path 119, thereby causingthe image stabilization control circuit 120 to execute the imagestabilization operation.

If it is not determined in Step 408 that the focus adjusting lens 111 islocated in the vicinity of the in-focus point and it is determined inStep 412 that the focus adjusting lens 111 is placed in an in-focusstate, the process proceeds to Step 412, in which the focus adjustinglens 111 is made to stop. To obtain a good, photographic image bypreventing a shake of the image due to, for example, a vibration of thecamera, the processing of Step 503 is executed so that the lens controlcircuit 118 communicates an instruction to execute an imagestabilization operation to the image stabilization control circuit 120through the communication path 119, thereby causing the imagestabilization control circuit 120 to execute the image stabilizationoperation.

As described above, if it is not determined in Step 408 that the focusadjusting lens 111 is located in the vicinity of the in-focus point andit is determined in Step 411 that the focus adjusting lens 111 is placedin the in-focus state, the process proceeds to Step 412, in which thefocus adjusting lens 111 is made to stop. After the focus adjusting lens111 has been made to stop, if it is determined in Step 411 that thefocus adjusting lens 111 has gone out of the in-focus state, the processproceeds to Step 413, in which it is determined whether it is necessaryto perform the operation of restarting the driving of the focusadjusting lens 111. The decision as to whether the restarting is neededcan be made by making a comparison between a focus voltage value atwhich it has been determined that the focus adjusting lens 111 is infocus and the current voltage value.

Specifically, in Step 413, if the difference between the focus voltagevalue at which it has been determined that the focus adjusting lens 111is in focus and the current focus voltage value is lower than apredetermined threshold, it is determined that the focus adjusting lens111 has gone out of the in-focus state, and a focus adjusting operation(the driving of the focus adjusting lens 111) is restarted. If the focusadjusting operation is to be restarted, it is necessary to eliminate anunnecessary variation in the focus voltage value so that the directionin which the focus adjusting lens 111 is to be driven can be determinedor the degree of defocus can be confirmed to set an accurate drivingspeed of the focus adjusting lens 111. For this reason, if it isdetermined in Step 413 that it is necessary to restart the focusadjusting operation, the processing of Step 504 is executed so that thelens control circuit 118 communicates an instruction to stop the imagestabilization operation to the image stabilization control circuit 120through the communication path 119, thereby stopping the imagestabilization operation.

If it is not determined in Step 413 that it is necessary to restart thefocus adjusting operation, this indicates that the focus adjusting lens111 is held in the in-focus state. Accordingly, the processing of Step503 is executed so that the lens control circuit 118 communicates aninstruction to execute an image stabilization operation to the imagestabilization control circuit 120 through the communication path 119,thereby causing the image stabilization control circuit 120 to executethe image stabilization operation.

By performing the above-described process, it is possible to preventwasteful power consumption by stopping the image stabilization operationduring the largely out-of-focus state in which no image stabilizationeffect can be obtained, and it is also possible to realize a focusadjusting operation free of malfunction by preventing an unnecessaryvariation in the focus voltage value during the restarting. Further, ifthe focus adjusting lens is in focus or in the vicinity of an in-focuspoint at which the contour of an image is sharp and a remarkable, imagestabilization effect can be visually confirmed in the image plane, theimage stabilization operation is executed so that it is possible toprevent a degradation of the image due to, for example, a vibration ofthe camera, or a malfunction of a focus adjusting device. Accordingly,it is possible to perform an efficient image stabilization operationaccording to the state of focus so that it is possible to consistentlyperform a good, photographic operation.

The second embodiment of the present invention will be described below.

Although, in the first embodiment, the operation of the imagestabilization device is controlled (executed or stopped) according tothe state of focus, the second embodiment is intended to realize asmoother operation control not by merely turning on or off the imagestabilization device but by varying the response performance andoperating characteristics of the image stabilization device.Specifically, the second embodiment can be used in the case of a largelyout-of-focus state in which it is desired to obtain an imagestabilization effect by causing a light deflecting lens to perform acertain extent of light deflecting operation.

The arrangement of the second embodiment is similar to that of the firstembodiment shown in FIG. 4, and further description thereof is omitted.The second embodiment differs from the first embodiment in respect ofthe processing of the instruction outputted from the lens controlcircuit 118 to the image stabilization control circuit 120. FIG. 6 is aflowchart showing a process to be executed by the lens control circuit118.

The second embodiment is arranged to vary the response performance ofthe image stabilization operation of the aforesaid image stabilizationdevice. If the image stabilization effect is low, the responseperformance of the image stabilization operation of the imagestabilization device is made low, whereas if a sufficient imagestabilization effect is obtained, the response performance is set to itsnormal state. To switch the response performance between the low stateand the normal state, it is preferable to use, for example, a loop gainwhich is switchable between two levels. In this case, during the normalstate, the loop gain is kept high to enhance the response performance,whereas, during the low state in which the image stabilization effect islow, the loop gain is kept low to lower the response performance. Withsuch loop gain, it is possible to obtain a certain extent of imagestabilization operation even in the case of a largely out-of-focusstate, and it is possible to realize a good, photographic operation as awhole without adversely affecting the operation of the automatic focusadjusting device during the largely out-of-focus state.

Referring to FIG. 6, if the focus adjusting lens 111 is located in thevicinity of the in-focus point (Step 408), the process proceeds to Step601, in which the response performance of the image stabilizationoperation is set to the normal state. Similarly, if the focus adjustinglens 111 is in focus (Step 411), the response performance of the imagestabilization operation is set to the normal state in Step 603. Thus, ineither of the steps 601 or 603, it is possible to obtain a sufficientimage stabilization performance.

If the focus adjusting lens 111 is largely out of focus (Step 405), theprocess proceeds to Step 602, in which the response performance of thelight deflecting operation of the light deflecting lens 101 forperforming the image stabilization operation is made low. Similarly, ifa decision is to be made as to the direction in which the focusadjusting lens 111 is to be driven for restarting purpose (Step 414),the response performance of the light deflecting operation of the lightdeflecting lens 101 for performing the image stabilization operation ismade low in Step 604. Thus, in either of the steps 602 or 604, it ispossible to obtain a certain extent of image stabilization operationwhile preventing the automatic focus adjusting system from beingadversely affected.

In the description of the first embodiment, reference has been made tothe arrangement in which the lens control circuit 118 controls the imagestabilization control circuit 120 so that the image stabilizationoperation can be executed or stopped. In the description of the secondembodiment, reference has been made to the arrangement in which the lenscontrol circuit 118 controls the image stabilization control circuit 120so that the response performance can be kept normal or made low.However, if the focus decision described in connection with theflowchart of each of FIGS. 5 and 6 is made up of a greater number offine steps or if it is desired to prepare far finer control modes, it isalso possible to suitably combine the above-described contents of thefirst and second embodiments so that the image stabilization operationcan be formed by a plurality of steps each corresponding to apredetermined amount of image stabilization and the response performancecan vary step by step between the stopped and normal states of the imagestabilization operation. Such an arrangement can also be encompassed inthe scope of the present invention without departing from the gistthereof.

Although each of the first and second embodiments has been describedwith reference to the camera having optical image stabilization means,problems similar to those described previously are also present in anarrangement in which a video signal subjected to electronic imagestabilization processing is used for focus adjustment. However,whichever of optical image stabilization and electronic imagestabilization may be adopted, it is possible to achieve similar effectsby stopping or executing the image stabilization operation according tothe degree of defocus or by adjusting the amount of the imagestabilization operation. Accordingly, the present invention can bedirectly applied to a camera having electronic image stabilizationmeans.

As is apparent from the foregoing description, according to either ofthe first and second embodiments, in an apparatus arranged to performautomatic focus adjustment while referring to an image modified by anoptical image stabilization device, it is possible to accuratelydetermine the direction or degree of defocus even in the case of a lowfocus voltage value by the provision of means for stopping a lightdeflecting operation during a largely out-of-focus state or the like andexecuting the light deflecting operation when a focus adjusting lens islocated at an in-focus point or in the vicinity of the in-focus point.Since no large image stabilization effect can be visually observedduring the largely out-of-focus state or the like, even if the imagestabilization operation is stopped, no performance is influenced so thatit is possible to prevent wasteful battery consumption.

What is claimed is:
 1. A camera comprising:image pickup means; vibrationdetecting means for physically detecting a vibration of a camera body;correcting means for correcting a motion of an image due to thevibration on the basis of information about the vibration detected bysaid vibration detecting means; focus detecting means for detecting astate of focus on the basis of a predetermined signal component of animage signal output by said image pickup means; and controlling meansfor controlling a correcting operation of said correcting meansaccording to the state of focus detected by said focus detecting meansto prevent an erroneous focal adjustment by said focus detecting means.2. A camera according to claim 1, wherein said controlling meanscontrols execution and restrains the correcting operation of saidcorrecting means according to the state of focus detected by said focusdetecting means.
 3. A camera according to claim 2, wherein saidcontrolling means stops the correcting operation of said correctingmeans when the state of focus is a largely out-of-focus state.
 4. Acamera according to claim 1, wherein said vibration detecting meanscomprises an angular-velocity sensor.
 5. A camera according to claim 1,wherein said correcting means comprises a variable angle prism.
 6. Acamera according to claim 1, wherein said focus detecting means detectsthe state of focus on the basis of a level of a high-frequency componentof a picked-up image signal.
 7. A camera comprising:image pickup means;vibration detecting means for detecting a vibration of a camera body;correcting means for optically correcting a motion of an image due tothe vibration on the basis of information about the vibration detectedby said vibration detecting means; focus detecting means for detecting astate of focus on the basis of a predetermined signal component of animage signal output by said image pickup means; and controlling meansfor controlling a characteristic of a correcting operation of saidcorrecting means according to the state of focus detected by said focusdetecting means to prevent an erroneous focal adjustment by said focusdetecting means.
 8. A camera according to claim 7, wherein saidcontrolling means controls a response characteristic of a vibrationcorrecting operation of said correcting means according to the state offocus detected by said focus detecting means.
 9. A camera according toclaim 8, wherein said controlling means controls an amount of correctionto be executed by said correcting means, by varying a control loop gainof said correcting means according to the state of focus detected bysaid focus detecting means.
 10. A camera according to claim 9, whereinsaid controlling means lowers the loop gain of said correcting meanswhen the state of focus is a largely out-of-focus state.
 11. A cameraaccording to claim 7, wherein said vibration detecting means comprisesan angular-velocity sensor.
 12. A camera according to claim 7, whereinsaid correcting means comprises a variable angle prism.
 13. A cameraaccording to claim 7, wherein said focus detecting means detects thestate of focus on the basis of a level of a high-frequency component ofa picked-up image signal.
 14. A video camera comprising:image pickupmeans; shake detecting means for detecting a shake; correcting means foroptically correcting a motion of an image due to the shake on the basisof information about the shake detected by said shake detecting means;focus detecting means for detecting a state of focus on the basis of apredetermined signal component of an image signal output from said imagepickup means; and controlling means for controlling a correctingoperation of said correcting means according to the state of focusdetected by said focus detecting means to prevent an erroneous focaladjustment by said focus detecting means.
 15. A video camera accordingto claim 14, wherein said controlling means controls execution and stopof the correcting operation of said correcting means according to thestate of focus detected by said focus detecting means.
 16. A videocamera according to claim 15, wherein said controlling means stops thecorrecting operation of said correcting means when the state of focus isa largely out-of-focus state.
 17. A video camera according to claim 14,wherein said controlling means controls a response characteristic of thecorrecting operation of said correcting means according to the state offocus detected by said focus detecting means.
 18. A video cameraaccording to claim 17, wherein said controlling means controls an amountof correction to be executed by said correcting means, by varying acontrol loop gain of said correcting means according to the state offocus detected by said focus detecting means.
 19. A video cameraaccording to claim 18, wherein said controlling means lowers the loopgain of said correcting means when the state of focus is a largelyout-of-focus state.
 20. A video camera according to claim 14, whereinsaid vibration detecting means comprises an angular-velocity sensor. 21.A video camera according to claim 14, wherein said correcting meanscomprises a variable angle prism.